Peripheral RAFT polymerization on covalent organic polymer with enhanced aqueous compatibility for controlled generation of singlet oxygen.

The efficient generation of singlet oxygen has attracted a great deal of interest in various fields such as medicine, synthetic chemistry and materials science. In this study, a covalent organic polymer (COP) is prepared by crosslinking the photosensitizer 4,4',4'',4'''-(porphyrin-5,10,15,20-tetrayl)tetraaniline (TAPP) with 4,4'-(anthracene-9,10-diyl)dibenzoic acid (ADDA) via the 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC)/4-dimethylaminopyridine (DMAP) coupling method. The COP is further modified with a hydrophilic polymer i.e. poly(poly(ethylene glycol) methyl ether methacrylate) through grafting-from reversible addition-fragmentation chain transfer (RAFT) polymerization to enhance its solubility in various solvent systems. The modified COP can bind with singlet oxygen through the formation of endoperoxide by ADDA upon the exposure to the red light irradiation. The singlet oxygen incorporated in COP can be then released via the photodynamic mechanism or the cycloreversion by endoperoxide when heated at 110 degrees C. Our results have opened new possibilities for simultaneous generation of singlet oxygen by the dual mechanisms, i.e. photodynamic route and singlet oxygen carrier, which demonstrates the promising potential for treating hypoxic tumors.